Waterproof microphone and associated packing techniques

ABSTRACT

Aspects of the disclosure provide a waterproof packaging technique for fabricating waterproof microphones in mobile devices. A device based on the waterproof packaging technique can include a microelectromechanical system (MEMS) device, a housing enclosing the MEMS device, and a liquid-resistant air inlet passive device (LRAPD) on the housing. The LRAPD can include at least one channel connecting an exterior of the housing with a chamber formed between the housing and the MEMS device. An inside surface of the channel can be coated with a liquid-repellant coating. In some examples, the liquid-repellant coating can be a self-assembled monolayer (SAM) coating.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of U.S. ProvisionalApplication No. 62/257,092, “Pressure Sensor Packaging Design for WaterProof Applications” filed on Nov. 18, 2015, and U.S. ProvisionalApplication No. 62/397,186, “A Directional Microphone and PackagingTechnique for Creating the Directional Microphone” filed on Sep. 20,2016, both of which are incorporated herein by reference in theirentirety.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

The mobile communication industry is evolving at a fast phase. One partof the evolution is the introduction of wristwatch mobile phones.Because wristwatch mobile phones are worn on wrists, certain componentsof the wristwatch mobile phones are more likely to be exposed to liquiddamage than that of normal mobile phones which are usually kept in aprotective environment (e.g. pockets). Even for normal mobile phones,there are components that have to be exposed to the outside environment.An example of the above mentioned components is the acoustic pressuresensor in a microphone for sensing sound wave pressure. These componentshave to be protected from being exposed to external damaging factors,such as rains or water, in order to operate properly.

Further, surrounding system noises can severely degrade voice quality ofa microphone, and therefore a directional microphone offers better voicequality due to its ability to only pick up sound signals in a certaindirection. However, a majority of mobile devices use omnidirectionalmicrophones due to unavailability of cost effective directionalmicrophones. In addition, electronic noise-canceling techniques used inomni-directional or directional microphones often fail to keep up withchanges in noise and are thus unable to effectively cancel backgroundnoise.

SUMMARY

Aspects of the disclosure provide a waterproof packaging technique whichcan be used for fabricating waterproof microphones in mobile devices.The waterproof packaging technique employs a liquid-resistant air inletpassive device (LRAPD) which can include a liquid-repellant channel andcan be attached to an opening in a housing enclosing an acousticpressure sensor. In one example, the inner surface of the LRAPD iscoated with a self-assembled monolayer (SAM) to realize the waterprooffunction.

A device based on the waterproof packaging technique can include amicroelectromechanical system (MEMS) device, a housing enclosing theMEMS device, and a liquid-resistant air inlet passive device (LRAPD) onthe housing. The LRAPD can include at least one channel connecting anexterior of the housing with a chamber formed between the housing andthe MEMS device. An inside surface of the channel can be coated with aliquid-repellant coating. In some examples, the liquid-repellant coatingcan be a self-assembled monolayer (SAM) coating. The LRAPD can beattached to an inner side of the housing with an inlet of the channelconnected to an opening in the housing, or attached to an outer side ofthe housing with an outlet of the channel connected to an opening in thehousing. Alternatively, the LRAPD can be disposed in an opening of thehousing.

In one example, the LRAPD includes multiple channels connecting anexterior of the housing with the chamber, and surfaces of the multiplechannels are coated with a liquid-repellant coating. In some examples,the housing can include a cover over a substrate supporting the MEMSdevice, and the LRAPD can be disposed on the substrate.

The MEMS device can be a pressure sensor, such as a piezoresistivepressure sensor, a capacitive pressure sensor, and the like in variousexamples. In one example, the MEMS device is an acoustic pressure sensorwith a sensing surface facing the chamber for sensing an acoustic wave,and the LRAPD is formed in a direction of the sensing surface to allowthe acoustic wave to reach the sensing surface without dampening theacoustic wave. In another example, a surface of a diaphragm opposite thesensing surface faces the chamber, and the LRAPD is configured toprovide an air pressure in the chamber that is equal to atmosphericpressure. Accordingly, in one example, the LRAPD includes a zigzagchannel.

In a further example, the acoustic pressure sensor includes a cavitybetween the sensing surface and a housing with an opening in the housingconnecting the cavity with the exterior of the housing, and the LRAPDcovers the opening.

In one example, the LRAPD includes a zigzag channel. In another example,the LRAPD includes a cavity proximate the channel to collect liquid. Ina further example, the MEMS device is an acoustic pressure sensor with asensing surface facing the chamber, and the channel of the LRAPDincludes a portion sloping from one end to the other end with respect tothe sensing surface to allow an acoustic wave to reach the sensingsurface. In one example, the MEMS device is an acoustic pressure sensorwith a sensing surface facing the chamber, and the channel of the LRAPDincludes a longest portion running parallel from a first end to a secondend with respect to the sensing surface to allow an acoustic wave toreach the sensing surface.

Aspects of the disclosure provide another packaging technique for makinga directional microphone. The packaging technique employs mechanicalstructures to cancel undesired background noise to realize directionalpicking up functions instead of requiring an extra sensor in electronicnoise-cancelling techniques. Accordingly, the packaging techniqueenables a directional microphone with reduced a footprint and cost.

A directional microphone device based on the packaging technique caninclude an acoustic sensor and a housing enclosing the acoustic sensor.The acoustic sensor can include a sensing diaphragm for sensing soundpressure, a cavity below the sensing diaphragm, and a first substrate.The directional microphone device can further includes a channel with aninlet open at an edge of the first substrate and an outlet connectedwith the cavity. The housing can include a cover attached to a secondsubstrate supporting the first substrate. The cover can include a firstopening over the sensing diaphragm and a second opening at a side of thecover. The second opening can be disposed adjacent to the inlet of thechannel.

In some examples, a first distance of a first path from the secondopening to the sensing diaphragm via the channel is configured to beequal to a second distance of a second path from the second opening tothe sensing diaphragm via a chamber between the cover and the acousticsensor.

In some examples, the directional microphone device includes multiplechannels each having an inlet open at the edge of the first substrateand an outlet connected with the cavity. The multiple channels canextend from the cavity to the edge of the first substrate, and can beevenly distributed from each other. In some examples, the cover includesmultiple second openings at sides of the cover. The multiple secondopenings can be evenly distributed along the edge of the cover. Inaddition, in some examples, the multiple second openings are positionedadjacent to respective inlets of the multiple channels.

The acoustic sensor can be fabricated with MEMS technology. The acousticsensor can be a capacitive pressure sensor, or a piezoresistive pressuresensor, and the like. In some examples, the microphone device caninclude an anechoic chip disposed over the cover and configured toabsorb sound waves reaching the anechoic chip.

In one example, the first substrate is bonded to the second substrate.In another example, the channel is formed between the first substrateand the second substrate. In a further example, the first substrate andthe second substrate are a same substrate made from a silicon wafer.

In one example, the second substrate further includes a barrier walldisposed outside the housing at an edge of the second substrate andadjacent to the second opening outside the housing. In one example, thebarrier wall is configured to block sound waves inside the housing fromleaving the housing, and to block sound waves outside the housing fromentering the housing.

In one example, the acoustic sensor includes sidewalls attached to thesensing diaphragm and the first substrate to form the cavity. In anotherexample, the first substrate includes an opening below the cavity. In afurther example, the sensing diaphragm is attached to the firstsubstrate, and the cavity is positioned within the first substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of this disclosure that are proposed as exampleswill be described in detail with reference to the following figures,wherein like numerals reference like elements, and wherein:

FIG. 1 shows a waterproof device according to some examples of thedisclosure;

FIG. 2A shows a sectional view of a liquid-resistant air inlet passivedevice (LRAPD) having a horizontal middle portion according to someexamples;

FIG. 2B shows a sectional view of another LRAPD having a sloping middleportion according to some examples;

FIG. 3A shows a top view of a first example of a LRAPD;

FIG. 3B shows a top view of a second example of a LRAPD;

FIG. 4A shows a section view of a third example of a LRAPD;

FIG. 4B shows a section view of a fourth example of a LRAPD;

FIG. 5 shows a top view and a side view of a fifth example of a LRAPD;

FIG. 6 shows an example of a fabrication process sequence forfabricating a LRAPD;

FIG. 7 shows a pressure sensor device using the waterproof packagingtechnique described herein according to some examples;

FIG. 8 shows structural variations of LRAPDs according to some examples;

FIG. 9 shows another pressure sensor device using the waterproofpackaging technique described above according to some examples;

FIG. 10 shows a further pressure sensor device using the waterproofpackaging technique described herein according to some examples;

FIG. 11 shows structures of an example LRAPD;

FIG. 12 shows another pressure sensor device using the waterproofpackaging technique described above according to some examples;

FIG. 13A shows an example of a sound pressure sensor based on capacitivesensing in a first operating state;

FIG. 13B shows an example of a sound pressure sensor based on capacitivesensing in a second operating state;

FIG. 14 shows an example of an omnidirectional microphone device;

FIG. 15A shows a capacitive pressure sensor with sound pressure exertedon one side of a sensing surface;

FIG. 15B shows how sound pressures of two synchronized sound waves arecancelled at a capacitive pressure sensor;

FIG. 16 shows an example capacitive pressure sensor for illustrating aprinciple for making a directional microphone;

FIG. 17 shows a sectional view of an example unidirectional microphonedevice according to some examples;

FIG. 18 shows a sectional view of an example substrate structure;

FIG. 19 shows a perspective view of an example unidirectional microphonedevice;

FIG. 20A shows an example of a unidirectional microphone device in asectional view;

FIG. 20B shows an example of a unidirectional microphone device in aperspective sectional view;

FIG. 20C shows an example of a unidirectional microphone device in aperspective view; and

FIG. 21 shows an example directional microphone device with LRAPDsaccording to some examples.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a waterproof device 100 according to some examples of thedisclosure. The device 100 includes a microelectromechanical system(MEMS) device 130, a cover 120, and a substrate 140. The cover 120 andthe substrate 140 form a housing 160 enclosing the MEMS device 130. Achamber 161 is thus formed between the cover 120 and the MEMS device130. The housing 160 can prevent outside particles, for example, waterdroplets, dust, and the like, from entering the chamber 161 to damagethe MEMS device 130 or degrade performance of the MEMS device 130.

The housing 160 includes an opening 121 that provides a passageconnecting the chamber 161 with the environment outside the housing 160.For example, the MEMS device 130 can be an acoustic pressure sensor forsensing a sound waves coming from outside the housing 160. The opening121 can provide a path for the sound waves to reach the MEMS device 130.

According to an aspect of the disclosure, in dry air applications, suchas air pressure sensors used in mobile phones, walkie-talkies, orwristwatch mobile phones, a sensing surface of the MEMS device 130 needsto be exposed to ambient environment to receive a sound wave pressure,or/and an opposite surface of the sensing surface needs to be vented tothe atmosphere in order to operate properly. At the same time, the MEMSdevice 130 needs to be protected from damage caused by liquid, such aswater, in the ambient environment. To serve this purpose, a waterproofpacking technique is provided in the disclosure. Specifically, aliquid-resistant air inlet passive device (LRAPD) 110 is employed forpackaging the device 100. As shown, the LRAPD 110 is attached to thecover 120 below the opening 121. The LRAPD 110 includes aliquid-resistant channel 111 which connects the chamber 161 with theopening 121 providing a path between the outside environment and theinterior of the housing 160. The liquid-resistant channel 111 exposes orvents the MEMS device 130 to the air while repulsing any liquid fromentering into the chamber 161.

In some pressure sensing applications, a waterproof gel coating can beused to cover an outer surface of a pressure sensor, such as the MEMSdevice 130 in FIG. 1, to protect the pressure sensor. However, forultra-low pressure sensing applications, such as microphones for soundpressure sensing, thickness of a sensing diaphragm of a pressure sensoris in a range of a few micrometers, and any gel coating may deteriorateperformance of such type of pressure sensor. In such scenario, a LRAPD110 can be more advantageous than a gel coating on the pressure sensor.

In various examples, the MEMS device 130 enclosed by the housing 160 canbe any suitable MEMS devices which utilizes exposure to externalenvironment of the housing 160. Generally, an MEMS device contains partsor components of a size ranging from 1 micrometer to 1 millimeter thatperform engineering functions by electromechanical means. A MEMS devicecan include micro sensors or actuators made of micromechanicalstructures, and auxiliary integrated circuits for device functioncontrols and signal transductions. In some examples, the MEMS device 130is configured to be a pressure sensor, such as a capacitive pressuresensor, a piezoresistive pressure sensor, and the like. Specifically, insome examples, the MEMS device 130 is configured to be acoustic pressuresensor for sensing a sound wave pressure.

In one example, the substrate 140 is a part of the MEMS device 130. Forexample, the substrate 140 is a portion of a silicon wafer which is usedfor fabricating one or more parts of the MEMS device 130, and the cover120 is bonded and sealed to the substrate 140 to form the chamber 161.In another example, the MEMS device 130 is fabricated on a silicon diethat is attached to the substrate 140 that is a part of a packaginghousing, and the cover 120 is then sealed to the packaging substrate 140to form the chamber 161. In the above two examples, the cover or thepackage housing can be made of any suitable materials, such as plastics,metals, ceramics, glass, and the like.

In various examples, the MEMS device 130 can include additionalmicroelectronics 150 (e.g., electronic circuits or components)cooperating with the MEMS device 130 to fulfill various functions.

FIG. 2A shows a sectional view of a LRAPD 200A according to someexamples. The LRAPD 200A includes a channel 201. The channel 201includes a first portion 210, a second portion 220 (a middle portion)and a third portion 230 sequentially connected to form the channel 201.In one example, the middle portion is perpendicular to the first portion210 and the third portion 230 as shown in FIG. 2A. The channel 201includes an inlet 211 and an outlet 231. In one example, the channel isformed in a piece of silicon material 250. The LRAPD 200A furtherincludes a liquid-repellant coating 240 covering at least part or all ofan inner surface of the channel 201. In addition, a size 202 of thechannel 201 (e.g., diameter of the channel) can vary depending onrequirements of various applications. In some examples, size of achannel in a LRAPD can be in a range of 2-50 micrometers, while in otherexamples, size of a channel in a LRAPD can be in a range of 50-500micrometers.

According to an aspect of the disclosure, the liquid-repellant coating240 can cause the hydrophobic effect when a water droplet is disposed atthe surface of the liquid-repellant coating 240 such that the dropletwater tends to form a spherical shape. As a result, when the size of thewater droplet is larger than the size 202 of the channel 201, the waterdroplet will be repelled from entering the channel 201. For example,when the LRAPD 200A is installed proximate an opening of a housingenclosing an acoustic pressure sensor for a mobile device, waterdroplets caused by rain or other ambient factors will be repelled fromentering the housing when the mobile device is exposed to the ambientenvironment. In some instances, it is possible that water droplets witha smaller size may enter through the inlet 211, however, these can beprevented from passing further through the channel 201 due to theliquid-repellant coating 240 and the structure of the channel 201.

In some examples, the liquid-repellant coating 240 is made of aself-assembled monolayer (SAM) coating, for example, generated from awet chemistry based process. In one example, the SAM coated surface ofthe channel 201 is extremely hydrophobic, and water contact angles thusformed can be greater than 90°. In addition, the thickness of a SAMcoating can be molecularly thin and in a range of 2-3 nanometers.

FIG. 2B shows a sectional view of another LRAPD 200B according to someexamples. The LRAPD 200B includes a channel 262 that has an inlet 261and an outlet 263 at two ends of the channel 262. The channel 262includes a first portion 264, a second portion 265 (a middle portion)and a third portion 266 sequentially connected to form the channel 262.The LRAPD 200B can also include a liquid-repellant coating covering atleast part or all of an inner surface of the channel 262. The channel262 can be formed in a piece of silicon material 250. However, differentfrom FIG. 2A example, the second portion 265 of the channel 262 slopesfrom one end to the other end.

In one example, the LRAPD 200B is attached to a cover and is parallel toa sensing surface of an MEMS device. Accordingly, the middle portion 265is sloped with respect to the sensing surface of the MEMS device 130. Inone example, the LRAPD includes a cavity 270 below the bottom portion ofthe channel 262 for collecting water passing through the inlet 261. Inthis way, the water inside the channel 262 will not block sound wavesfrom passing through the channel 262. The stored water may laterdisappear gradually through evaporation. In one example, absorbentmaterials are filled in the cavity for holding liquid. The absorbentmaterials can include Polyvinyl Alcohol (PVA) sponges, polyestersponges, and the like. In other examples, the LRAPD may not include thecavity and in the case that a water droplet having a size smaller thanthat of the inlet 261 enters the channel 262, the water droplet can beretained at a bottom portion at the lower end of the second portion 265.As a result, the water droplet is prevent from further going through thechannel 262 after entering through the inlet 261 due to the slopedchannel.

It is noted that a LRAPD can have various configurations depending onpackaging requirements of various applications. For example, the channelcan be in any form and shape. The size and length of the channel canvary depending on the application. For devices likely to be subject towetter conditions, the channel can be made longer to reduce liquidabsorption and transfer into the chamber of the housing. For devicesless likely to be subject to wet conditions, the channel can be shorterto reduce manufacturing costs. The number of channels of a LRAPD can belarger than one. The channel can be either strait or zigzag, or anyother forms. In addition, a LRAPD can be mounted outside or inside ahousing enclosing a MEMS device, or in the plane of an opening in thehousing thus being merged with the housing. When mounted outside thehousing, the outlet of the LRAPD can be aligned with an opening of thehousing, while when mounted inside the housing the inlet of the LRAPDcan be aligned with the opening of the housing. Further, in someexamples, an opening in a housing can be positioned at any suitablelocations, for example, top, bottom, or side of the housing, fordisposing a LRAPD proximate the opening. Furthermore, a LRAPD can bemade of any suitable materials in addition to silicon materials, such asplastics, metals, ceramics, glass, polysilicon, silicon dioxide, and thelike.

FIGS. 3A/3B/4A/4B/5 show some examples of LRAPDs with different designs.FIG. 3A shows a top view of a first version of a LRAPD 300A. The LRAPD300A includes an inlet 301 opening upward, an outlet 303 facingdownward, and two separate channels 302 arranged in parallel connectingwith the inlet 301 and the outlet 303 at opposite ends. FIG. 3B shows atop view of a second version of a LRAPD 300B. Similarly, the LRAPD 300Bincludes an inlet 311 opening upward, an outlet 313 facing downward anda channel 312 connecting with the inlet 311 and the outlet 313. However,the channel 312 has a zigzag form, and is longer and narrower thaneither one of the channels 302. Accordingly, the LRAPDs 300A and 300Bcan be used for different purposes in acoustic pressure sensors. Forexample, the LRAPD 300A can be used for exposing sound pressure to asensing surface of a pressure sensor such that the sound wave pressurecan reach the sensing surface without being hindered. In contrast, theLRAPD 300B can be used for venting a chamber behind the sensing surfaceto the atmosphere such that the chamber has an air pressure equal to theatmospheric pressure.

FIG. 4A shows a section view of a third version of a LRAPD 400A. TheLRAPD 400A includes a channel 402 that has a zigzag form in verticaldirection. Due to the vertical zigzag structure, when a water dropletenters the channel 402 from an inlet 401, the water droplet can beretained at a bottom portion 410 of the channel 402, thus reducingpossibility for the water droplet to reach an outlet 403 of the channel402. The retained water droplet can evaporate later. FIG. 4B shows asection view of a fourth version of a LRAPD 400B which has a formsimilar to that of the LRAPD 400A. The LRAPD 400B includes a channel 422having an inlet 421 and an outlet 423. The channel 422 may have a bottomportion 430 as shown in FIG. 49. However, different from LRAPD 400A, theLRAPD 400B may additionally include a cavity 440 at below the bottomportion 430. The cavity 440 can function as a liquid reservoir forreceiving water droplets entering the inlet 421 and storing the receivedwater temporarily. In this way, more water droplets can be retained atthe cavity, and sound waves can still pass through the channel 422without being blocked by the retained water. Water stored in the cavity440 can later evaporate into the atmosphere and/or the cavity 440 canstore a material such as a sponge to absorb liquid.

FIG. 5 shows a top view and a side view of a fifth version of a LRAPD500 on the left and right side of FIG. 5, respectively. The LRAPD 500takes a form of a square chip with multiple channels 501 going throughthe chip from one side to another side. In various examples, the length,size, number and position arrangement of the multiple channels 501 mayvary. This allows sound to travel through the LRAPD 500 while preventingor hindering liquid from passing through to the interior chamber. Thethird version LRAPD 500 provides multiple channels 501 for sound wavesgoing through without being dampened. An application example of thethird version LRAPD 500 is shown in FIG. 12.

FIG. 6 shows an example of a fabrication process sequence 600 forfabricating a LRAPD. Standard semiconductor processing technology can beused to fabricate a LRAPD in some examples. The fabrication processsequence 600 can include multiple steps, and diagrams (a) to (e) in FIG.6 represent part of the multiple steps.

First, a first silicon wafer 601 is prepared as shown in diagram (a).The silicon wafer 601 can be of any suitable type as known by one ofordinary skill in the art. Second, a channel 602 is patterned and etchedin the first wafer 601 as shown in diagram (b). Third, optionally, asilicon oxide layer can be grown on the entire first wafer 601. Next, asshown in diagram (c), a second wafer 603 can be bonded over the firstwafer 601 thus forming a channel 602. Similarly, the second wafer 603can be of any suitable types. Any suitable bonding mechanisms can beused for the fabrication. Then, both wafers 601 and 603 can be grounddown into a thin substrate such that thickness of the LRAPD is reduced.This step can be optional and the thickness of the final LRAPD can varydepending on interior space of a housing enclosing a MEMS device. Next,as shown in diagram (d), air inlet ports 604 and 605 are etched in bothwafers 601 and 603 at the opposite ends of the channel 602 to form achannel 606. Finally, as shown in diagram (e), a SAM coating is formedon all or part of the inner surface of the channel 606, the inlet 604and outlet 605.

It is noted that silicon materials are used in the FIG. 6 example,however fabrication of a LRAPD is not limited to silicon materials. Anysuitable materials, such as plastics, metals, ceramics, and the like,can be used for fabricating a LRAPD with various fabrication processes.

FIG. 7 shows a pressure sensor device 700 using the waterproof packagingtechnique described herein according to some examples. The device 700can include a housing 710 formed by a cover 711 and a substrate 712, anda pressure sensor 720 enclosed in the housing 710. In addition, anopening 713 can be formed on the cover 721, and a LRAPD 701 is disposedin the opening 713. The LRAPD 701 can include one or more channelscoated with a liquid-repellant coating, such as a SAM coating.

In various examples, the pressure sensor 720 can be an absolute, gage ordifferential measurement device. Generally, a pressure sensor measures acertain pressure in comparison to a reference pressure, and pressuresensors can be categorized into three types of devices: absolute, gageand differential devices. Absolute pressure sensors measure the pressurewith respect to a high vacuum reference sealed in a cavity behind asensing diaphragm. Gage pressure sensors measure the pressure relativeto ambient atmospheric pressure. Differential pressure sensors measure adifference between two pressures on opposite sides of a sensingdiaphragm. For gage pressure sensor, one side opposite the sensing sideof the diaphragm has to be exposed to atmospheric pressure. In addition,the pressure sensor 720 can be sensors based on various physicalmechanisms. For example, the pressure sensor 720 can be a capacitivepressure sensor or a piezoresistive sensor in different examples.

In FIG. 7, a capacitive pressure sensor 720 is used as an example forillustrating the waterproof technique. The capacitive pressure 720 isfabricated with MEMS technology and includes micromechanical structures.As shown, the capacitive pressure sensor 720 includes a diaphragm(moving plate) 721 and a back plate (fixed plate) 722. Two electrodesattached to the diaphragm 721 and the back plate 722 form a capacitor.The back plate 722 is perforated such that a cavity 723 below the backplate 722 is connected with the gap between the diaphragm 721 and theback plate 722. In addition, the capacitive pressure sensor 720 isattached to the substrate 712 by some sealing materials 724. In oneexample, the capacitive pressure sensor 720 is fabricated on a silicondie separated from a silicon wafer that includes multiple units ofpressure sensors generated from a fabrication process.

While the air is allowed to go through the LRAPD 701, water droplets canbe prevented from entering the housing 710 due to liquid-resistantfunction of the LRAPD 701.

In one example, the capacitive pressure sensor 720 is configured to bean acoustic pressure sensor 720 performing gage pressure measurement.The acoustic pressure sensor 720 includes a venting path (not shown)which provides a path allowing air coming from the opening 713 to enterthe cavity 723. At the same time, the air coming from the opening 713can also reach the sensing surface (upper surface in FIG. 7). As aresult, both the sensing surface and back surface (bottom surface inFIG. 7) of the diaphragm 721 are exposed to the same atmosphericpressure, which provides a condition required for gage pressuremeasurement. In another example, the capacitive pressure sensor 720 is abarometric pressure sensor 720 performing absolute pressure measurement.Accordingly, the chamber 723 may be sealed to form a vacuum.

In one example, the capacitive pressure sensor 720 is an acousticpressure sensor 720 for sensing sound wave pressure, and the device 700is configured to be a microphone, for example, used in a mobile device.During the operation of the acoustic pressure sensor 720, sound pressureis allowed to enter the housing 710 through a channel of the LRAPD 701and reach the sensing surface of the diaphragm 721. As a response, thediaphragm 721 vibrates according to changes of sound pressure exerted onthe diaphragm 721 and causes variations in capacitance value of thecapacitor formed by the diaphragm 721 and the back plate 722. Thechanges in capacitance value can be subsequently measured by auxiliarymicroelectronics of the device 700 and reflected in a current or voltagesignal processed by the device.

FIG. 8 shows several diagrams illustrating structure variations ofLRAPDs according to some examples. LRAPDs with these structures can beused in FIG. 7 example. As shown, diagram (a) is a cross sectional viewof a LRAPD 810 which includes an inlet 811 and a channel 812. A channelformed by the inlet 811 and the channel 812 provides a path 814 for asound wave to pass through the LRAPD 810 and enter the housing 710.Diagram (b) shows a cross sectional view of another LRAPD 820 whichincludes an inlet 821, a channel 821, and an outlet 823. A channelformed by the inlet 821, the channel 821, and the outlet 823 provides apath 824 for a sound wave entering the housing 710.

Diagrams (d) and (e) show two different tunnel structures 830 and 850 intop view that can be used in either of the channels 812 and 822.Accordingly, diagrams (c) and (f) shows cross sectional views of the twochannel structures 830 and 850 respectively. As shown, the channelstructure 830 has only one channel, while the channel structure 850 hasmultiple channels 851.

It is noted that dimensions of the channel of the LRAPD 701 can bedetermined according to requirements of specific applications. Forexample, in applications of acoustic pressure sensing, such asmicrophones in a mobile device, the LRAPD 701 is used to expose soundwave to the sensing surface of the diaphragm 721. In order to preventwater droplets from entering the housing 710, the cross section size ofa channel of the LRAPD 701 needs to be smaller than a certain dimension.On the other side, the dimension of the channels of the LRAPD 701 needsto be large enough to allow the sound wave going through without dampingor distorting the sound wave. Accordingly, in one example, a LRAPD withthe channel structure 850 having multiple channels 851 can be employed.The multiple channels 851 together provide a broad passage for the soundwave while each channel 851 has a size small enough for repelling waterdroplets. In another example, a LRAPD with the structure 840 having asingle channel that has a narrow cross section is employed. In oneexample, the cross section area of a channel in the LRAPD is selected tobe less than a circle with a diameter of 10 micrometers. In anotherexample, the dimension of a channel in the LRAPD is determined to be ina range of 10-100 micrometers. In addition to numbers and size ofchannels in the LRAPD 701, the length of the channels of the LRAPD 701can be determined to be relatively short such that the sound wave canreach the sensing surface without being dampened.

FIG. 9 shows another pressure sensor device 900 using the waterproofpackaging technique described above according to some examples. Thedevice 900 has similar structure as the device 700 except that anopening 913 is positioned on a substrate 912 of the device 900, and aLRAPD 901, as illustrated for example in FIGS. 2-8, is disposed at theopening 913. Accordingly, air pressure is exposed to a pressure sensor920 through the LRAPD 901 in the substrate 912. This design can furtherinhibit the entry of liquid into the chamber by being on an underside ofthe pressure sensor device 900.

FIG. 10 shows a further pressure sensor device 1000 using the waterproofpackaging technique described herein according to some examples. Thedevice 1000 includes a housing 1010 formed by a cover 1011 and asubstrate 1012, and a pressure sensor 1020 enclosed in the housing 1010.A chamber 1014 is formed between the cover 1011 and the pressure sensor1020. In addition, the substrate 1012 includes a first opening 1013, asecond opening 1025, and a LRAPD 1001 disposed at the first opening1013.

In one example, the pressure sensor 1020 is a piezoresistive pressuresensor 1020. In another example, the pressure sensor 1020 is acapacitive pressure sensor 1020. FIG. 10 shows a structure of thecapacitive sensor 1020 that is used as an example to illustrate thewaterproof packaging technique. As shown, the capacitive sensor 1020includes a diaphragm 1021 and a perforated back plate 1022. Two metallayers (not shown) each attached to the diaphragm 1021 or the back plate1022 form two electrodes of a capacitor for sensing operation. A cavity1023 is formed below the diaphragm 1021, while the back plate 1022 ispositioned above the diaphragm 1021. In addition, the second opening1025 in the substrate 1012 connects the cavity 1023 to the ambientatmosphere. In one example, at least part of the sensing surface (bottomsurface in FIG. 10) of the diaphragm 1021 and at least part of thesurface of the sidewalls surrounding the cavity 1023 are coated with aSAM coating.

In some examples, the capacitive sensor 1020 performs gage pressuremeasurement. Accordingly, the chamber 1014 is exposed to the atmospherepressure through the LRAPD 1001 such that back side (upper side in FIG.10) of the diaphragm 1021 is exposed to the atmosphere pressure. Thesensing surface (lower side in FIG. 10) of the diaphragm 1021 isdirectly exposed to the atmosphere pressure through the second opening1025.

In one example, the pressure sensor 1020 is an acoustic pressure sensor1020 performing gage pressure measurement, and the device 1000 isconfigured to be a microphone, for example, used in a mobile device.Accordingly, sound wave pressure passing through the second opening 1025is sensed by the diaphragm 1021, while atmosphere pressure is vented tothe chamber 1014 through the first opening 1013. Because there is noneed to allow sound waves to enter the chamber 1014, the LRAPD 1001proximate to the first opening 1013 can have a single channel with asmall cross section area and a long length. FIG. 11 shows structures ofan example of the LRAPD 1001 in several diagrams (a) to (c).

Diagram (a) shows a cross sectional view of a LRAPD 1110 including aninlet 1111, a channel 1112, and an outlet 1113 which form a channel1114. The channel 1114 provides a path for sound waves to pass through.Diagrams (b) and (c) shows a top view 1120 and a sectional view 1130 ofthe channel 1114, respectively. As shown, the channel 1114 includes asingle channel 1121 which can be long such that sound waves may beprevented from entering the chamber 1014 while atmospheric pressure isvented into the chamber 1014.

FIG. 12 shows another pressure sensor device 1200 using the waterproofpackaging technique described above according to some examples. Thedevice 1200 has similar structures as the device 1000 in FIG. 10.However, the device 1200 includes another LRAPD 1202 in addition to aLRAPD 1201. Specifically, the device 1200 includes a housing 1210enclosing a pressure sensor 1220. A cavity 1223 is formed below adiaphragm 1221 of the pressure sensor 1220, and an opening 1225 connectsthe cavity 1223 to the ambient environment. The LRAPD 1201 vents achamber 1214 between the housing 1210 and the pressure sensor 1220 toambient atmosphere. The LRAPD 1202 is disposed over the opening 1225 toprevent water droplets from entering the cavity 1223 while allowing airgoing into the cavity 1214.

In one example, the device 1200 is configured to be a microphone and thepressure sensor 1220 is an acoustic pressure sensor for sensing soundwaves. In order to expose the sensing surface of the diaphragm 1221 tosound waves without damping or distorting the sound waves, the LRAPD1202 can have a structure similar to that in FIG. 5 where multiplechannels 501 are provided for exposing the sound waves to the diaphragm1221.

The pressure sensor devices described above can be applied to variousapplications, such as sound pressure sensing, barometric pressuremeasurement, manifold pressure sensing, and the like. However, it isnoted that the water proof packaging techniques and the LRAPDs describedabove are not limited to pressure sensor devices or pressure sensorapplications, and can be used for other devices and applicationswherever ambient atmosphere is to be exposed to interior of the deviceswhile liquid droplets are prevented from entering the interior of thedevices.

Generally, an omnidirectional microphone is able to pick up sound fromall directions, and may be unsuitable for certain applications where theenvironment is very noisy. For example, when a driver sitting inside avehicle speaks towards a hands-free mobile phone, an omnidirectionalmicrophone in the mobile phone not only picks up his voice but alsopicks up all background sounds inside the vehicle thus reducing clarityof driver's voice at the other end of the line. For these applications,a cost effective directional microphone can be employed to mitigateeffects of background noise.

Directional microphones can be based on different techniques. Forexample, one approach is to electronically cancel out the backgroundnoise. However, such type of devices requires at least two soundpressure sensors to realize the noise cancellation function, whichenlarges device package footprint and increases cost due to an extrasensor element. In addition, auxiliary electronics performing electroniccancellation also do not effectively handle rapidly alternatingenvironmental sound waves.

Aspects of the disclosure provide a packaging technique for making adirectional microphone device. The packaging technique employs a certainmechanical structure to cancel environmental noise in contrast toelectronic noise cancellation method. The packaging technique does notrequire an extra sensor or electronic chip to realize directionalfunctions and serves the purpose of a cost effective directionalmicrophone.

A microphone is a sensing device which includes a sound pressure sensorfor measuring changes of sound pressure propagating in the air or othertypes of media. In some applications, the sound pressure is small interms of pressure scale and therefore a sound pressure sensor iscategorized as an ultra-low pressure sensor. A sound pressure sensor canbe based on various transduction mechanisms, such as capacitive sensing,piezoresistive sensing, and the like, and can be fabricated with varioustechnologies, such as MEMS technology or non-MEMS technology.

FIGS. 13A and 13B show an example of a sound pressure sensor 1300 basedon capacitive sensing. The capacitive sensor 1300 includes twoelectrodes (not shown) each attached to a diaphragm (a moving plate)1311 and a back plate (a fixed plate) 1312 with a small gap 1313 betweenboth electrodes, thus forming a capacitor. In FIG. 13A, no soundpressure is exerted on the diaphragm 1311, and the two plates 1311/1312of the sensor 1300 are parallel to each other. In FIG. 13B, a varyingsound pressure 1321 is exerted on the diaphragm 1311 and the diaphragm1311 moves accordingly towards or away from the fixed plate 1312, thuscausing deflections 1314 of the diaphragm 1311 and changing capacitancevalue of the capacitor. Changes of the capacitance value can beindicated, for example, by an output current of a circuit connected withthe capacitor. In this way, sound pressure variations can be measuredusing the capacitive sensor 1300.

FIG. 14 shows an example of an omnidirectional microphone device 1400.The microphone device 1400 includes a sound pressure sensor 1420, and ahousing 1410 enclosing the pressure sensor 1420. The housing 1410includes an opening 1411 for allowing sound waves entering the housing1410 and reaching a sensing surface 1423 of the sound pressure sensor1420. In one example, the sound pressure sensor 1420 is a capacitivesensor 1420 which includes a diaphragm 1421 and a perforated back plate1422. As shown, as the microphone device 1400 is omnidirectional, themicrophone 1400 picks up sounds 1431 entering the opening 1411 from alldirections including background noise, which reduces the clarity of aspeaker's voices.

FIGS. 15A and 15B shows how sound pressures of two synchronized soundwaves are cancelled at a capacitive pressure sensor 1500. The capacitivepressure sensor 1500 includes a diaphragm 1511, and a fixed plate 1512with a gap 1513 between the diaphragm 1511 and the fixed plat 1522, thusforming a capacitor. In FIG. 15A, when sound pressures 1521 are exertedon one side (upper side) of the diaphragm 1511, the diaphragm 1511deflects to deflecting positions 1514 accordingly. In FIG. 15B, however,when a pair of synchronized sound pressures 1521/1522 approaches bothsides of the diaphragm 1511 simultaneously, the pressures 1521/1522exerted on both sides cancel each other out. Accordingly, the diaphragm1511 does not move. The pair of synchronized sound pressures 1521/1522can be generated by two synchronized sound waves each exerting a varyingsound pressure 1521 or 1522 on opposite side of the diaphragm 1511 whilekeeping the two varying sound pressures 1521/1522 equal to each other.

FIG. 16 shows an example capacitive pressure sensor 1600 forillustrating a principle for making a directional microphone. Thecapacitive pressure sensor 1600 includes a diaphragm 1611 and a fixedplate 1612 which forms a capacitor, and the diaphragm 1611 moves as aresponse to a sound pressure exerted on the diaphragm 1611 causingcapacitance variation of the capacitor. Changing of the capacitanceincurs a varying output current or voltage signal indicating variationsof the sound pressure.

As shown, a sound wave 1620 is generated from a sound source A. A soundwave 1621, which is a portion of the sound wave 1620, approaches anupper side of the diaphragm 1611 from the direction perpendicular to thediaphragm 1611. The sound wave 1621 exerts a pressure on the upper sideof the diaphragm 1611. Another sound wave 1622, which is another portionof the sound wave 1620, propagates along a route 1623 and approaches alower side of the diaphragm 1611. Due to a delay caused by passing alongthe route 1623, the sound waves 1621 and 1622 are not synchronized whenreaching opposite sides of the diaphragm 1611. Accordingly, soundpressures of the two sound waves 1621 and 1622 exerted on opposite sidesof the diaphragm 1611 will not cancel each other, and the sound pressureof the sound wave 1621 can thus be detected.

As shown, a sound wave 1630 a is generated from a sound source B, andtwo sound waves 1631 a/1631 b, each of which is a portion of the soundwave 1630, approaches opposite sides of the diaphragm 1611. As the twosound waves 1631 a/1631 b are generated from the same source B, andreaches opposite sides of the diaphragm 1611 at the same time via pathshaving the same length, the two sound waves 1631 a/1631 b synchronizeswith each other and will cancel each other. As a result, pressuresimposed on the two opposite sides of the diaphragm 1611 by the soundwaves 1631 a/1631 b will not contribute to deflections of the diaphragm1611. Similarly, sound waves 1632 a/1632 b, which are portions of asound wave 1630 a generated from a third sound source C, will not bereflected in the varying output signal.

As a result, the sound wave 1621 from the perpendicular directiondeflects the diaphragm 1611 and can be sensed by the capacitive pressuresensor 1600 while sound waves from other directions, such as the soundwaves 1630 a/1630 b, will not be sensed due to the cancellation effect.When a microphone is configured in a way showed in FIG. 16 that soundwaves are allowed to approach a sensing surface from a directionperpendicular to the sensing surface, or approach opposite sides of thesensing surface via two equal-length routes from other directions, themicrophone can have a directional sensing ability which picks up soundfrom the perpendicular direction while canceling sound from otherdirections.

The principle illustrated in FIG. 16 can be employed to create adirectional microphone. Accordingly, a packaging technique based on theprinciple is described herein to make a cost effective unidirectionalmicrophone. The packaging technique is illustrated with examples shownin FIGS. 17-21. The examples in FIGS. 17-21 are based on MEMStechnologies, but the packaging technique is not exclusive to MEMSmicrophone and it can also be used with other types of microphonefabricated with non-MEMS technologies.

It is also noted that although capacitive pressure sensors are used asexamples for illustrating the principle and the packaging technique formaking a directional microphone in FIGS. 16-21, the principle and thepackaging technique are not limited to capacitive pressures sensors. Anysensors based on other transduction mechanisms with a sensing diaphragmcapable of receiving a sound wave at both sides can be used for makingdirectional microphones based on the principle and packaging techniquedescribed herein. For example, a directional microphone can be made of apiezoresistive pressure sensor.

FIG. 17 shows a sectional view of an example unidirectional microphonedevice 1700 according to some examples. The device 1700 includes a cover1712 and a first substrate 1730 which form a housing 1724 enclosing anacoustic pressure sensor 1716. A chamber 1746 is formed between thecover 1724 and the acoustic pressure sensor 1716. In one example, thefirst substrate 1730 is a part of the acoustic pressure sensor 1716. Forexample, the first substrate 1730 is a portion of a silicon wafer whichis used for fabricating one or more parts of the acoustic pressuresensor 1716, and the cover 1712 is later bonded and sealed to the firstsubstrate 1730 to form the housing 1724. In another example, theacoustic pressure sensor 1716 is fabricated on a silicon die that isbonded to the first substrate 1730 that is a part of a packaginghousing, and the cover 1712 is then sealed to the packaging substrate1730 to form the housing 1724. In the above two examples, the cover 1712or the package housing 1724 can be made of any suitable materials, suchas plastics, metals, ceramics, glass, and the like. In some examples,the first substrate 1730 can include one or more electrical contacts1702 for establishing connections, for example, with a print circuitboard (PCB).

The acoustic pressure sensor 1716 can be a capacitive pressure sensor, apiezoresistive sensor, and the like, and can be a sensor based on MEMStechnology or non-MEMS technology. In one example, the acoustic pressuresensor 1716 includes a sensing diaphragm 1722 which can move as aresponse to a sound pressure exerted on the sensing diaphragm 1722. Theacoustic pressure sensor 1716 may further include a fixed plate in otherexamples, such as the capacitive sensors in FIGS. 7, 9, 10 and 12,although not shown in FIG. 17, for performing capacitive sensing.

In one example, the acoustic pressure sensor 1716 further includes acavity 1736 below the sensing diaphragm 1722. For example, in the FIG.17 example, the acoustic pressure sensor 1716 includes one or moresidewalls 1732 below the sensing diaphragm 1722 that support the sensingdiaphragm 1722 at the edge of the sensing diaphragm 1722, and enclosingthe cavity 1736 below the sensing diaphragm 1722. In addition, loweredges of the sidewalls 1732 are attached to a second substrate 1726which includes an opening 1738 connected to the cavity 1736. Then, thesecond substrate 1726 is attached to the first substrate 1730. Thus, thesensing diaphragm 1722, the sidewalls 1732, the second substrate 1726,and the first substrate 1730 enclose the cavity 1736.

It is to be appreciated that in various designs, the cavity 1736 can beformed with various structures. For example, the acoustic pressuresensor 1716 may not include structure of the sidewalls 1732 and thesensing diaphragm 1722 may be disposed directly over the opening 1738 ofthe second substrate 1726. For another example, the second substrate1726 may not include an opening 1738, thus enclosing the cavity 1736from below. For a further example, the second and third substrate 1726and 1730 may be one substrate, for example, fabricated from one siliconwafer.

In one example, the acoustic pressure sensor 1716 includes the secondsubstrate 1726. The second substrate 1726 includes one or more channels1734 a/1734 b connecting the cavity 1736 with exterior of the acousticpressure sensor 1716. In one example, an outlet at one end of eachchannel is connected with the cavity 1736 and an outlet at the other endof each channel is opened at the edge of the second substrate 1726 asshown in FIG. 17. Each of the one or more channels 1734 a/1734 bprovides a path for sound waves to reach the cavity, and subsequentlythe lower side of the sensing diaphragm 1722, from exterior of theacoustic sensor 1716.

It is noted that although only two channels 1734 a/1734 b are shown inFIG. 17, there can be more than two channels crossing the secondsubstrate 1726, for example, 6, 8, 20, and any other suitable numbers ofchannels. In addition, in one example, the multiple channels can beevenly distributed and extend from the cavity 1736 or the opening 1738to the edge of the second substrate 1726.

In one example, the acoustic pressure sensor 1716 further includes anauxiliary integrated circuit 1714. The auxiliary integrated circuit 1714can be used for conditioning or controlling operations of the acousticpressure sensor 1716, or the auxiliary integrated circuit 1714 caninclude circuitry, such as a pre-amplifier, for processing a signalgenerated at the acoustic pressure sensor 1716.

As shown in FIG. 17, the cover 1712 can include two types of openingsfor allowing sound pressures entering the housing 1724 and reaching thesensing diaphragm 1722. A first opening 1720 is positioned above thesensing diaphragm 1722 such that sound waves from the first opening 1720reach the sensing diaphragm 1722 from above the sensing diaphragm 1722.One or more second openings 1708 a/1708 b are positioned at the edge ofthe cover 1712 where the cover 1712 is bonded to the first substrate1730 in one example. In addition, in one example, second openings 1708a/1708 b are positioned adjacent to entrances 1735 a/1735 b of channels1734 a/1734 b. For example, the second opening 1708 a is adjacent to theentrance 1735 a of the channel 1734 a, while the second opening 1708 bis adjacent to the entrance 1735 b of the channel 1734 b. Accordingly,when sound waves enter the housing 1724 from a second openings 1708a/1708 b, the sound waves can have two separate paths to reach oppositesides of the sensing diaphragm 1722: one path is through a channel 1734a/1734 b to reach the lower side of the sensing diaphragm 1722, andanother path is through the chamber 1746 to reach the upper side of thesensing diaphragm 1722.

In operation, the device 1700 can pick up a sound 1718 entering thefirst opening 1720 while a sound 1728 entering second openings 1708a/1708 b is being cancelled. Specifically, as an example shown in FIG.17, a first portion of the sound 1718 entering the first opening 1720approaches the upper side of the sensing diaphragm 1722 from a directionperpendicular to the sensing diaphragm 1722. At the same time, a secondportion of the sound 1718 entering the first opening 1720 propagatesalong the route 1710 and reaches the lower side of the sensing diaphragm1722. The route 1710 passes the channel 1734 a as illustrated in FIG.17. The second portion of the sound 1718 is delayed due to the longsound travel route 1710. Accordingly, the first and second portion ofthe sound 1718 are not synchronized and do not cancel each other out.Thus, the sound 1718 can be detected by the sensor.

In contrast, the sound 1728 entering the second opening 1708 b caninclude a first portion and a second portion which reach the upper sideand lower side of the sensing diaphragm 1722 via two different routes1744/1742 as shown in FIG. 17. The path 1744 is between the cover 1712and the acoustic sensor 1716, and the path 1742 is via the channel 1734b through the second substrate 1726. As shown, the two different routes1744/1742 can have approximately the same distance, and no delay orsmall delay is introduced between the first and second portion of thesound 1728. Accordingly, the first and second portion of the sound 1728will cancel each other out, and thus the sound 1728 cannot be detectedby the sensor.

In one example, the first substrate 1730 includes a first barrier wallstructure 1704 and second barrier wall structure 1706 for blocking soundwaves inside the housing 1724 from leaving the housing. As a result,interferences caused by sound waves leaving the housing 1724 andsubsequently reentering the housing 1724 can be avoided. As shown, inone example, the barrier wall structures 1704/1706 is disposed proximatethe second openings 1708 a/1708 b such that sound waves from inside thehousing 1724 will be reflected back to the housing 1724. It also reducessounds from various angles from entering the housing 1724.

It is noted that, in order to cancel pressures generated by sound wavesentering the housing 1724 through a second opening 1708 a in the cover1712, a length of a channel 1734 a can be determined in such a way thatthe length of the channel 1734 a is equal to or approximately equal to alength of a route from the second opening 1708 a to the upper side ofthe sensing diaphragm 1722. Under such a configuration, two portions ofa sound wave entering the second opening 1708 a will reach the upperside and lower side of the sensing diaphragm 1722, respectively, at asame time thus being synchronized to each other. As a result, soundpressures of the two portions are cancelled by each other.

FIG. 18 shows a sectional view of an example substrate structure 1800.The substrate structure 1800 corresponds to a combination of the firstsubstrate 1726 and the second substrate 1730 shown in FIG. 17. As shown,the substrate structure 1800 includes a first substrate 1810 and asecond substrate 1820 corresponding to the first substrate 1726 and thesecond substrate 1730 shown in FIG. 17. The second substrate 1820 caninclude an opening 1821 connected with the cavity 1736 in FIG. 17. Thesecond substrate 1820 can further include two channels 1822 a and 1822 bextending from the edge of the second substrate 1820 to the opening1821, thus each providing a path 1823 a or 1823 b for sound wavesreaching the opening 1821.

In addition, the first and second substrate 1810 and 1820 can be bondedtogether, for example, by some adhesive materials 1841. In one example,a gap 1840 is formed between the two substrates 1810 and 1820. However,in another example, no gap exists between the two substrates 1810 and1820. In various examples, the first substrate 1810 can be a printcircuit board (PCB), a part of a packing housing, a silicon chip, andthe like, and the second substrate 1820 can be a silicon die, or a chipmade of suitable materials.

FIG. 19 shows a perspective view of an example unidirectional microphonedevice 1900. As shown, a sound pressure sensor 1901 is packaged within ahousing 1910. The housing 1910 includes a cover 1912 attached to asubstrate 1914. A first opening 1916 is positioned over the sensor 1901at the top of the cover 1912. In one example, the position of the firstopening 1916 is close to one side of the microphone and away from themiddle of the cover 1912. In addition, multiple second openings 1918 arepositioned along the edge of the cover 1912 where the cover 1912 and thesubstrate 1814 adjoin to each other. In operation, sounds entering thefirst opening 1916 can be picked up by the sensor 1901, while soundsentering the second openings 1918 will not be sensed by the sensor 1901due to the cancellation effect discussed previously.

FIGS. 20A/20B/20C show an example of a unidirectional microphone device2000 in sectional view, perspective sectional view, and perspectiveview, respectively. An anechoic chip 2040 is mounted on top of a cover2012 of the device 2000 in order to reduce interference to a sensingoperation of the device 2000.

The device 2000 includes a first substrate 2011 the cover 2012 whichencloses an acoustic pressure sensor 2020. The sensor 2020 includes asensing diaphragm 2021, a cavity 2023 below the sensing diaphragm 2021surrounded be sidewalls 2022. The sensor 2020 also includes a secondsubstrate 2030, and auxiliary electronics 2024. The second substrate2030 includes an opening 2032 below the cavity 2023. The secondsubstrate 2030 further includes multiple channels 2031 a-2031 d, each ofwhich has an inlet at the outer edge of the second substrate 2030 and anoutlet connected with the cavity 2023 below the sensing diaphragm 2021.

In addition, the device 2000 includes a first opening 2014 in the cover2012 above the sensing diaphragm 2021, and multiple second openings 2013at the edge of the cover 2012 where the cover 2012 adjoins to the firstsubstrate 2011.

As shown, the anechoic chip 2040 is mounted on top of the cover 2012,and includes an opening 2043 over the opening 2014 in the cover 2012. Inone example, the anechoic chip 2040 is coated with a porous layer 2041for deadening sound. The porous layer 2041 can include minute cavitiesor holes 2042 on its surface for trapping incoming sound. The structureof the minute spaces or holes can be various in various examples. Forexample, the minute cavities 2042 can be formed by rectangular studsdensely arranged in orthogonal directions, densely arranged cones, orcombination of different structures.

It is noted that mounting anechoic chips is optional when packaging aunidirectional microphone. In addition, an anechoic chip can be mountedbeneath the surface of top side of a cover where the top surface has anopening to hold and expose the anechoic chip.

FIG. 21 shows an example directional microphone device 2100 with LRAPDsaccording to some examples. The device 2100 has similar structure as thedevice 1700 in FIG. 17. However, multiple LRAPDs are employed to protectthe sensor 1716 from water droplet damaging. Specifically, a LRAPD 2110is disposed proximate to the first opening 1720, while multiple LRAPDs2120 a/2120 b are disposed proximate to the second openings 1708 a/1708b. In one example, these LRAPDs 2110/2120 a/2120 b are configured toallow sound pressures to reach the sensing diaphragm without dampeningthe corresponding sound waves. Thus, short and broad channels may beemployed in these LRAPDs 2110/2120 a/2120 b.

As describes, aspects of the disclosure provide a waterproof packagingtechnique which can be used for fabricating waterproof microphones inmobile devices. The waterproof packaging technique employs aliquid-resistant air inlet passive device (LRAPD) which can include aliquid-repellant channel and can be attached to an opening in a housingenclosing an acoustic pressure sensor. In one example, the inner surfaceof the LRAPD is coated with a self-assembled monolayer (SAM) to realizethe waterproof function.

A device based on the waterproof packaging technique can include amicroelectromechanical system (MEMS) device, a housing enclosing theMEMS device, and a liquid-resistant air inlet passive device (LRAPD) onthe housing. The LRAPD can include at least one channel connecting anexterior of the housing with a chamber formed between the housing andthe MEMS device. An inside surface of the channel can be coated with aliquid-repellant coating. In some examples, the liquid-repellant coatingcan be a self-assembled monolayer (SAM) coating. The LRAPD can beattached to an inner side of the housing with an inlet of the channelconnected to an opening in the housing, or attached to an outer side ofthe housing with an outlet of the channel connected to an opening in thehousing. Alternatively, the LRAPD can be disposed in an opening of thehousing.

In one example, the LRAPD includes multiple channels connecting anexterior of the housing with the chamber, and surfaces of the multiplechannels are coated with a liquid-repellant coating. In some examples,the housing can include a cover over a substrate supporting the MEMSdevice, and the LRAPD can be disposed on the substrate.

The MEMS device can be a pressure sensor, such as a piezoresistivepressure sensor, a capacitive pressure sensor, and the like in variousexamples. In one example, the MEMS device is an acoustic pressure sensorwith a sensing surface facing the chamber for sensing an acoustic wave,and the LRAPD is formed in a direction of the sensing surface to allowthe acoustic wave to reach the sensing surface without dampening theacoustic wave. In another example, a surface of a diaphragm opposite thesensing surface faces the chamber, and the LRAPD is configured toprovide an air pressure in the chamber that is equal to atmosphericpressure. Accordingly, in one example, the LRAPD includes a zigzagchannel.

In a further example, the acoustic pressure sensor includes a cavitybetween the sensing surface and a housing with an opening in the housingconnecting the cavity with the exterior of the housing, and the LRAPDcovers the opening.

In one example, the LRAPD includes a zigzag channel. In another example,the LRAPD includes a cavity proximate the channel to collect liquid. Ina further example, the MEMS device is an acoustic pressure sensor with asensing surface facing the chamber, and the channel of the LRAPDincludes a portion sloping from one end to the other end with respect tothe sensing surface to allow an acoustic wave to reach the sensingsurface. In one example, the MEMS device is an acoustic pressure sensorwith a sensing surface facing the chamber, and the channel of the LRAPDincludes a longest portion running parallel from a first end to a secondend with respect to the sensing surface to allow an acoustic wave toreach the sensing surface.

As described, aspects of the disclosure provide another packagingtechnique for making a directional microphone. The packaging techniqueemploys mechanical structures to cancel undesired background noise torealize directional picking up functions instead of requiring an extrasensor in electronic noise-cancelling techniques. Accordingly, thepackaging technique enables a directional microphone with reduced afootprint and cost.

A directional microphone device based on the packaging technique caninclude an acoustic sensor and a housing enclosing the acoustic sensor.The acoustic sensor can include a sensing diaphragm for sensing soundpressure, a cavity below the sensing diaphragm, and a first substrate.The directional microphone device can further includes a channel with aninlet open at an edge of the first substrate and an outlet connectedwith the cavity. The housing can include a cover attached to a secondsubstrate supporting the first substrate. The cover can include a firstopening over the sensing diaphragm and a second opening at a side of thecover. The second opening can be disposed adjacent to the inlet of thechannel.

In some examples, a first distance of a first path from the secondopening to the sensing diaphragm via the channel is configured to beequal to a second distance of a second path from the second opening tothe sensing diaphragm via a chamber between the cover and the acousticsensor.

In some examples, the directional microphone device includes multiplechannels each having an inlet open at the edge of the first substrateand an outlet connected with the cavity. The multiple channels canextend from the cavity to the edge of the first substrate, and can beevenly distributed from each other. In some examples, the cover includesmultiple second openings at sides of the cover. The multiple secondopenings can be evenly distributed along the edge of the cover. Inaddition, in some examples, the multiple second openings are positionedadjacent to respective inlets of the multiple channels.

The acoustic sensor can be fabricated with MEMS technology. The acousticsensor can be a capacitive pressure sensor, or a piezoresistive pressuresensor, and the like. In some examples, the microphone device caninclude an anechoic chip disposed over the cover and configured toabsorb sound waves reaching the anechoic chip.

In one example, the first substrate is bonded to the second substrate.In another example, the channel is formed between the first substrateand the second substrate. In a further example, the first substrate andthe second substrate are a same substrate made from a silicon wafer.

In one example, the second substrate further includes a barrier walldisposed outside the housing at an edge of the second substrate andadjacent to the second opening outside the housing. In one example, thebarrier wall is configured to block sound waves inside the housing fromleaving the housing, and to block sound waves outside the housing fromentering the housing.

In one example, the acoustic sensor includes sidewalls attached to thesensing diaphragm and the first substrate to form the cavity. In anotherexample, the first substrate includes an opening below the cavity. In afurther example, the sensing diaphragm is attached to the firstsubstrate, and the cavity is positioned within the first substrate.

While aspects of the present disclosure have been described inconjunction with the specific embodiments thereof that are proposed asexamples, alternatives, modifications, and variations to the examplesmay be made. Accordingly, embodiments as set forth herein are intendedto be illustrative and not limiting. There are changes that may be madewithout departing from the scope of the claims set forth below.

What is claimed is:
 1. A device, comprising: a microelectromechanicalsystem (MEMS) device; a housing enclosing the MEMS device, wherein achamber is formed between the housing and the MEMS device, the chamberis a single continuous space fluidically connected to an exterior of thehousing, the MEMS device is a rectangle in a sectional view, the chamberis in contact with at least three sides of the rectangle in thesectional view of the MEMS device; and a liquid-resistant air inletpassive device (LRAPD), the LRAPD being separate from the housing andattached to the housing, the LRAPD including at least one channelconnecting the exterior of the housing with the chamber.
 2. The deviceof claim 1, wherein the entire inside surface of the channel is coatedwith a liquid-repellant coating.
 3. The device of claim 2, wherein theliquid-repellant coating is a self-assembled monolayer (SAM) coating. 4.The device of claim 1, wherein the LRAPD is attached to an inner side ofthe housing with an inlet of the channel connected to an opening in thehousing.
 5. The device of claim 1, wherein the LRAPD is attached to anouter side of the housing with an outlet of the channel connected to anopening in the housing.
 6. The device of claim 1, wherein the LRAPD isdisposed in an opening of the housing.
 7. The device of claim 1, whereinthe LRAPD includes multiple channels connecting an exterior of thehousing with the chamber, and surfaces of the multiple channels arecoated with a liquid-repellant coating.
 8. The device of claim 1,wherein the housing includes a cover over a substrate supporting theMEMS device, and the LRAPD is attached to the cover.
 9. The device ofclaim 1, wherein the MEMS device is a pressure sensor.
 10. The device ofclaim 9, wherein the MEMS device is a piezoresistive pressure sensor.11. The device of claim 9, wherein the MEMS device is a capacitivepressure sensor.
 12. The device of claim 1, wherein the MEMS device isan acoustic pressure sensor with a sensing surface facing the chamber,and the channel of the LRAPD is formed in a direction of the sensingsurface to allow an acoustic wave to reach the sensing surface.
 13. Thedevice of claim 1, wherein the MEMS device is an acoustic pressuresensor with a surface of a diaphragm opposite a sensing surface facingthe chamber, and the LRAPD is configured to provide an air pressure inthe chamber which is equal to atmospheric pressure.
 14. The device ofclaim 13, wherein the acoustic pressure sensor includes a cavity betweenthe sensing surface and the housing with an opening in the housingconnecting the cavity with the exterior of the housing, and the LRAPDcovers the opening.
 15. The device of claim 1, wherein the LRAPDincludes a zigzag channel.
 16. The device of claim 1, wherein the LRAPDincludes a cavity proximate the channel to collect liquid.
 17. Thedevice of claim 1, wherein the MEMS device is an acoustic pressuresensor with a sensing surface facing the chamber, and the channel of theLRAPD includes a longest portion running parallel from a first end to asecond end with respect to the sensing surface to allow an acoustic waveto reach the sensing surface.
 18. The device of claim 1, wherein theMEMS device is an acoustic pressure sensor with a sensing surface facingthe chamber, and the channel of the LRAPD includes a portion slopingfrom one end to the other end with respect to the sensing surface toallow an acoustic wave to reach the sensing surface.